In the prior art, with respect to an image pickup element having pixels arranged thereon in a two-dimensional matrix, in order to fulfill a request to speed up the output of an image signal, the request being made in recent years, an image pickup element having pixels, each of which has an analog-digital conversion device arranged therein, is used. This image pickup device speeds up analog-digital conversion by concurrently performing the analog-digital conversion in all pixels. For example, there is proposed a system in which each pixel has an analog-digital conversion device arranged therein, the analog-digital conversion device including: a comparison unit that compares an analog image signal generated by a photodiode with a reference signal; and a latch that holds a digital signal generated on the basis of a result of the comparison.
Here, the reference signal is a signal, the voltage of which changes in a ramp-shaped manner, and is a signal that is commonly input into analog-digital conversion devices of all pixels arranged on an image pickup device. In the above-described system, the comparison unit compares the analog image signal with the reference signal. In addition, when a shift occurs from a low voltage state in which a voltage of the reference signal is lower than a voltage of the analog image signal to a high voltage state in which the voltage of the reference signal is higher than the voltage of the analog image signal, or when a shift occurs from the high voltage state to the low voltage state, a change in the voltage is detected, and is then output as a result of the comparison. Further, a code word that is a digital signal corresponding to the voltage of the reference signal is input into the latch, and the input code word is held in the latch on the basis of the detection result detected by the comparison unit. Subsequently, the code word held in the latch is output as a result of analog-digital conversion (for example, refer to Non-Patent Document 1).